From: "Peter Boyce" peterboyce at myjaring.net> on 2005.07.30 at 16:18:11(13256)Lemnaceae (Lemna, Landoltia, Spirodela,
Wolffia & Wolffiopsis) is now back in the Araceae as a sister clade to the
Pothoids - e.g., the lemnoids are unisexual flowered aroids.

The "scum" is actually a couple of really neat aroids. The tiny
(actually the smallest flowering plant) Wolffia can be identified along with
the larger Lemna by checking into Landolt's Lemnaceae, Fl. North America 22:
143-153. Oxford University Press (2000).